This present invention relates generally to manufacturing objects. More particularly, the invention provides a method and structure for hermetically bonding a transparent cover to a semiconductor substrate. Merely by way of example, the invention has been applied to a transparent glass cover hermetically bonded to a semiconductor wafer containing a micro-mechanical electrical system. The method and structure can be applied to display technology as well as, for example, charge coupled display camera arrays, and infrared arrays.
The packaging of silicon integrated circuits has reached a high level of maturity. FIG. 1 illustrates a simplified diagram of a conventional silicon integrated circuit package. The silicon integrated circuit die 110 is mounted on a submount 115 featuring a ball grid array 120. Wire bonds 125 are attached to the silicon die 110 to provide electrical connection to the submount 115. Typically, the silicon die 110 and the wire bonds 125 are encapsulated using a plastic encapsulant 130. The resulting package is robust and inexpensive.
The package illustrated in FIG. 1 presents several drawbacks in applications that often require more than electrical operation of the silicon integrated circuit. An example of such an application is optical reflection off an array of micro-mirrors or other MEMS structure. For example, these applications typically require the ability to illuminate the top of the silicon integrated circuit with optical energy and subsequently reflect the optical energy off the top of the silicon integrated circuit with high efficiency. The optical properties of the plastic encapsulant, including lack of transparency, non-uniformity of the index of refraction, and surface roughness make these packages unsuitable for this application. Additionally, many MEMS often require an open space above the surface of the silicon integrated circuit to enable the micro-electro-mechanical structures to move in the direction parallel to the plane of the MEMS as well as in the direction perpendicular to the plane of the MEMS. The physical contact that the plastic encapsulant makes with the surface of the integrated circuit, therefore, make this package unsuitable for many MEMS applications.